(3) باب مَنْ بَاعَ عَلَى الضَّعِيفِ وَنَحْوِهِ
Narrated Ibn `Umar:
A man was often cheated in buying. The Prophet (ﷺ) said to him, "When you buy something, say (to the seller), No cheating." The man used to say so thenceforward .
Reference: Sahih al-Bukhari 2414
In-book reference: Book 44, Hadith 5
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 3, Book 41, Hadith 597